Field effect type organic transistor and process for production thereof

ABSTRACT

A field effect type organic transistor is provided which comprises a source electrode, a drain electrode, and a gate electrode, a gate insulating layer, and an organic semiconductor layer, wherein the gate insulating layer contains an optical anisotropic material having an anisotropic structure formed by light irradiation, and the organic semiconductor layer is in contact with the anisotropic structure.

TECHNICAL FIELD

The present invention relates to a field effect type organic transistorand a process for production thereof. In particular, the presentinvention relates to a field effect type organic transistor useful inelectronic fields such as display devices, information tags, IC, and soforth, and to a process for production thereof.

BACKGROUND ART

Transistors employing an organic semiconductor are being developedactively in competition with silicon transistors based on crystallinesilicon technology. The organic semiconductor has features of an organicmaterial such as light-weight, flexibility, variety, and durability, andfurther has advantages that it can be formed by a low temperatureprocess of about 100° C. and can be produced by a liquid process such asprinting and spin coating. Therefore, the organic transistor can beformed on a plastic substrate, or in a larger display screen, which hasnot been achieved by crystal silicon semiconductors. Therefore theorganic transistor is promising in application to novel devices such asflexible electronic paper sheets, and information tags.

A usual organic semiconductor has a carrier mobility on a level of 10⁻⁴to 10⁻² cm²/Vs, which is lower by one or more decimal digits than insilicon semiconductors. Owing to this high resistance, a large currentis not readily obtainable and the operation frequency is lower,disadvantageously. For obtaining higher mobility, it is effective toarrange regularly the organic semiconductor layers to enlarge theoverlap of the conjugation planes as large as possible. A simple methodfor arranging a liquid crystal substance for a display element is arubbing method. In Patent Literature 1 (shown later), a fluorine typeamorphous polymer is laminated to an insulating oxide film, and thereonan organic semiconductor is arranged by rubbing treatment to achieve amobility of a level of 10⁻³ cm²/Vs.

On the other hand, to solve the problem of contamination of impuritycaused by the cloth and nonuniformity in the rubbing method, opticalorientation is disclosed in which the film is made anisotropic byirradiation with light for orientation. However, the optical orientationis applicable to limited kinds of liquid crystal materials as describedin Patent Literature 3.

Generally, in the field effect transistor, the drain current in thesaturation area can be derived according to Equation (I) below.Id=μ(W/2L)Ci(Vg−Vth)²   (I)where Id is a drain current (A), μ is a mobility (cm²/Vs), W is achannel breadth (cm), L is a channel length, Ci is a capacity (F/cm²) ofa gate insulating layer, Vg is a gate voltage (V), Vth is a thresholdvoltage of a transistor. The value of Vth is obtained by extrapolationin the relation of the square root of the drain current and the gatevoltage to the drain current Id=0.

In use of the transistor as a switching device, the ratio of the currentflowing between a source electrode and a drain electrode in a turned-onstate to that in a turned-off state (on-off ratio) should be not lessthan 10⁴, preferably is not less than 10⁶. However, in organicsemiconductors, the ion current is small owing to the low mobility asmentioned above and the off-current is large owing contamination in theorganic semiconductors. Therefore, sufficiently high on-off ratio is notobtainable with the organic semiconductors. The field effect typeorganic transistor employing an organic semiconductor does not satisfythe necessary practical characteristics at the moment.

Patent Literature 1 Japanese Patent Application Laid-Open No. H07-221367

Patent Literature 2 Japanese Patent Application Laid-Open No. H10-182821

Patent Literature 3 Japanese Patent Application Laid-Open No. 2001-40209

DISCLOSURE OF THE INVENTION

The present invention has been achieved on the above technical background to solve the above problems, and intends to provide a novel fieldeffect type organic transistor having an organic semiconductor layergiving a high mobility and a high on-off ratio useful in electronicfields for display devices, information tags, and IC.

The present invention intends to provide a field effect type of organictransistor giving an improved mobility and an improved on-off ratio ofthe organic semiconductor. This field effect type organic transistor isproduced by using a gate insulating layer containing an opticalanisotropic material and orienting an organic semiconductor material bythe optical anisotropic material.

According to an aspect of the present invention, there is provided afield effect type organic transistor comprising a source electrode, adrain electrode, a gate electrode, a gate insulating layer, and anorganic semiconductor layer, wherein the gate insulating layer containsan optical anisotropic material having an anisotropic structure formedby light irradiation, and the organic semiconductor layer is provided incontact with the anisotropic structure.

The anisotropic structure is formed preferably by optical isomerizationor dimerization.

The optical anisotropic material is preferably an azobenzene compound, acinnamoyl compound, a coumarine compound, or a chalcone compound.

The organic semiconductor layer is constituted preferably of aconjugated polymer compound.

The conjugated polymer compound has a weight-average molecular weightranging preferably from 5,000 to 500,000.

According to another aspect of the present invention, there is provideda process for producing a field effect type organic transistor having asource electrode, a drain electrode, a gate electrode, a gate insulatinglayer, and an organic semiconductor layer, the process comprising thesteps of forming the gate insulating layer containing an opticalanisotropic material, and forming the organic semiconductor layer incontact with an anisotropic structure formed by irradiation of light tothe optical anisotropic material.

The irradiating light is preferably ultraviolet light.

The irradiating light is preferably polarized ultraviolet light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a field effect type organictransistor of the present invention.

FIG. 2 is a schematic sectional view of a field effect type organictransistor employed in Example of the present invention.

FIG. 3 is a schematic sectional view of another field effect typeorganic transistor employed in Example of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The structure of the field effect transistor of the present invention iseffective in any of planar types, stagger types, and inverse staggeredtypes. The structure of the field effect type organic transistor of thepresent invention is explained by taking an example of planar type byreference to FIG. 1.

FIG. 1 is a schematic sectional view of an example of the field effecttype organic transistor of the present invention. In FIG. 1, the fieldeffect type organic transistor of the present invention is constitutedof an insulating substrate 11, gate electrode 12 thereon, gateinsulating layer 13 further thereon, source electrode 15 and drainelectrode 14 further thereon, organic semiconductor layer 16 furtherthereon, and protecting film 17 as the uppermost layer.

The field effect type organic transistor of the present inventioncontains an optical anisotropic material in the gate insulating layer,and the optical anisotropic material allows the contacting organicsemiconductor material to orient. This orientation gives the effects of(1) improvement of the mobility in the organic semiconductor, and (2)improvement of the on-off ratio.

The optical anisotropic material employed in the present invention canbe made anisotropic on the surface by action of light, and is capable oforienting the organic semiconductor material in contact therewith.

In an organic semiconductor layer, the direction of movement of thecharges is closely related to the conjugation plane of the organicsemiconductor material as described in “Nature”, vol. 401, 14, 685,1999. Therefore, for improvement of the mobility in the organicsemiconductor layer, it is important not only to uniformize thedirection of the organic semiconductor material but also to define theconjugation plane. A rubbing method is known to be the simplest and mosteffective method for orienting a liquid crystal. The rubbing method isapplicable to the organic semiconductor material as disclosed in theaforementioned Japanese Patent Application Laid-Open No. H07-221367.However, this method simply arranges molecules of an organicsemiconductor in a direction along grooves, but does not define theconjugation plane for the mobility. On the other hand, the opticalanisotropic material has been developed for orienting similarly a liquidcrystal material, but can only define to some extent a macroscopicdirection of the liquid crystal molecules in molecular movement withoutdefining the arrangement of the structure of the molecules.

In the present invention, it was found that an optical anisotropicmaterial, when used for orienting an organic semiconductor material, iscapable of defining the microscopic arrangement of the structure. Thiseffect cannot be obtained with a liquid crystal material. The advantagesof the present invention are as follows: (1) an organic semiconductormaterial can be arranged microscopically to define the conjugation planeby utilizing the interaction between the optical anisotropic materialand the organic semiconductor material in a micro region, enablingdefinition of a conjugation plane; (2) the interface between theinsulating layer and an organic semiconductor layer can be formed withless irregularity of the orientation and with high flatness; (3) Theoff-state current can be minimized owing to a less amount ofcontaminating dust and impurities; and so forth.

The optical anisotropic material employed in the present invention isnot limited, provided that the material is capable of causing anisotropyon the surface thereof to orient a contacting organic semiconductorlayer. The anisotropy-forming processes are classified roughly into twotypes: a photoisomerization type, and a photoreaction type. Thephotoreaction type is further classified into a dimerization type, adecomposition type, a combination type, and a decomposition-bridgingtype. Not to contaminate the organic semiconductor layer, the processesare preferred which do not leave impurity ions, radicals, or the likeafter the light irradiation. Accordingly, the photoisomerization typeand the dimerization type are preferred.

The photoisomerization type process utilizes an isomerization reactiontypified by cis-trans isomerization. Preferred materials are exemplifiedby azobenzene compounds. The azobenzenes rearrange from a trans form toa cis form by light irradiation of a wavelength of 365 nm, and rearrangefrom a cis form to a trans form by light irradiation of the wavelengthof 436 nm reversibly. The dimerization type process utilizes preferablycinnamoyl compounds, coumarine compounds, and chalcone compounds.

Specific examples of the optical anisotropic material employed in thepresent invention are enumerated below without limiting the invention.In the structural formulas below, R represents H, a halogen, CN, CF₃, oran alkyl or perfluoroalkyl group of 1 to 20 carbon atoms: in the alkyl,one or more of methylene groups may be replaced by O, CO, NH, or S. Xrepresents an alkylene group of 1 to 20 carbon atoms: in the alkylene,one or more of methylene groups may be replaced by O, CO, NH, or S. Arepresents —CH—CH₂—, —C(CH₃)—CH₂—, or —SiZ—O—: Z representing an alkylor alkoxy group of 1 to 20 carbons. The symbol n represents an integershowing a polymer, ranging from 10 to 100,000 corresponding to anumber-average polymerization degree.

The gate insulating layer containing the optical anisotropic material ofthe present invention can be comprised of an optical anisotropicmaterial by a process of casting, spin coating, immersion coating,screen printing, micromolding, microcontacting, roll coating,ink-jetting, LB forming, or the like.

The gate insulating layer of the present invention may be constituted ofone or more layers, and may be composed of combination of the opticalanisotropic material and another additional material. The additionalmaterial includes inorganic materials such as SiO₂, SiN, Al₂O₃, andTa₂O₅; organic materials such as polyimides, polyacrylonitrile,polytetrafluoroethylene, polyvinyl alcohol, polyvinylphenol,polyethylene terephthalate, and polyvinylidene fluoride; andorganic-inorganic hybrid materials, but is not limited thereto. Of thematerials, organic compounds are preferred because of possibility ofworking by a low-cost liquid process.

The process for producing the field effect type organic transistor ofthe present invention comprises a step of forming a gate insulatinglayer containing an optical anisotropic material; a step of irradiatingthe optical anisotropic material with light to give anisotropy to thesurface of the optical anisotropic material and to give it capability toorient an organic semiconductor material in contact with the gateinsulating layer; and a step of orienting the organic semiconductorlayer by utilizing the orientation-controlling capability of the opticalanisotropic material.

In the production process of the present invention, the light forirradiation of the optical anisotropic material includes visible light,ultraviolet light, and the like. Of these, ultraviolet light ispreferred, and polarized light such as linearly polarized light andelliptically polarized light is preferred. The polarized light can beobtained by passing the light generated by a high-pressure mercury lamp,a metal halide lamp, a xenon lamp, or the like through a polarizingfilter or a polarizing prism. The quantity of the light energy rangespreferably from 0.1 to 10 J/cm².

The material of the organic semiconductor layer in the present inventionmay be any conjugated compounds having a conjugated double bond withoutlimitation. The preferred compounds therefor include:

conjugated polymer compounds such as polyacetylene derivatives,polythiophene derivatives having a thiophene ring,poly(3-alkylthiophene) derivatives, poly(3,4-ethylenedioxythiophene)derivatives, polythienylene-vinylene derivatives, polyphenylenederivatives having a benzene ring, polyphenylenevinylene derivatives,polypyridine derivatives having a nitrogen atom, polypyrrolederivatives, polyaniline derivatives, and polyquinoline derivatives;oligomers such as dimethylsexithiophene, and quaterthiophene;

acenes such as perylene, tetracene, and pentacene; deposited organicmolecules such as copper phthalocyanine derivatives; discotic liquidcrystals such as triphenylene derivatives; smectic liquid crystals suchas phenylnaphthalene derivatives and benzothiazole derivatives; andliquid crystal polymers such as poly(9,9-dialkylfluorenebithiophene)copolymer; but are not limited thereto.

Of the above compounds, preferred are polymer compounds having theconjugation structure for production by a liquid phase process. Thepolymer compounds include compounds having the structures shown below.

(In the formulas, R₁, R₂, R₃, and R₄ represent respectively H, F, or analkyl or alkoxy group of 1 to 20 carbon atoms; and n represents apositive integer.)

The molecular weight of the above conjugated polymer compounds is notlimited, but preferably the weight-average molecular weight ranges from5,000 to 500,000 in view of the solubility in a solvent and thefilm-forming properties.

The organic semiconductor layer in the present invention may contain asuitable dopant for adjusting the electronic conductivity. The dopantincludes acceptor type dopants such as I₂, Br₂, Cl₂, ICl, BF₃, PF₅,H₂SO₄, FeCl₃, TCNQ (tetracyanoquinodimethane); donor type dopants suchas Li, K, Na, and Eu; and surfactants such as alkylsulfonic acid salts,and alkylbenzenesulfonic acid salts.

The insulating substrate is not limited in the constituting material.The material includes inorganic material such as glass, and quartz;photosensitive polymer compounds such as polymers of acryl types, vinyltypes, ester types, imide types, urethane types, diazo types, andcinnamoyl types; organic materials such as polyvinylidene fluoride,polyethylene terephthalate, and polyethylene; and organic-inorganichybrid materials. These materials may be laminated in two or more layersto increase the dielectric strength effectively.

The materials for the gate electrode, the source electrode, and thedrain electrodes in the present invention are not limited, provided thatthe material is electroconductive. The materials include metal materialssuch as Al, Cu, Ti, Au, Pt, Ag, and Cr; inorganic materials such aspolysilicon, silicides, ITO (indium tin oxide), and SnO₂;electroconductive polymer such as polypyridine, polyacetylene,polyaniline, polypyrrole, and polythiophene which are highly doped;electroconductive inks containing carbon particles, silver particles andthe like. In particular, for use for flexible electronic paper sheets,or the like, preferably each of the electrodes are comprised of anelectroconductive polymer, electroconductive inks containing carbon orsilver particles dispersed therein, or the like in order to make uniformthe thermal expansions with the substrate.

The processes for forming the respective members of the electrodes, thegate insulating layer, and the organic semiconductor layer are notlimited. In the case where an organic material is used, the member canbe formed by electrolytic polymerization, casting, spin coating,immersion coating, screen printing, micro-molding, micro-contacting,roll coating, ink-jetting, LB forming, or the like. Depending on thekind of the material used, vacuum vapor deposition, CVD, electron beamdeposition, resistance-heating vapor deposition, or sputtering iseffective.

The above members can be patterned in an intended shape byphotolithography and etching treatment. Otherwise, soft lithography andink-jetting are also effective in the patterning. Additionally, adrawing-out electrode, or a protection film may be formed, as necessary.

The present invention provides a field effect type of organic transistorgiving an improved mobility and an improved on-off ratio of the organicsemiconductor. The improvement is achieved by using a gate insulatinglayer containing an optical anisotropic material, and orienting theorganic semiconductor material by the optical anisotropic material. Thefield effect type organic transistor is useful in electronic fields suchas display devices, information tags, IC, and so forth, and a processfor production thereof.

EXAMPLE 1

The present invention is explained below in more detail by reference toexamples without limiting the invention.

FIG. 2 is a schematic sectional view of the field effect type organictransistor employed in the example of the present invention. Gateelectrode 21 was a highly doped n-type silicon substrate. Sourceelectrode 23 and drain electrode 24 were comprised of gold. Organicsemiconductor layer 25 was comprised of copper phthalocyanine shown bythe formula below.

Gate insulating layer 22 was comprised of azobenzene compound A shownbelow.

The azobenzene compound A was synthesized according to the methoddescribed in Japanese Patent No. 3163357. The obtained azobenzenecompound A had a weight-average molecular weight of 5.5×10⁵ and a Tg of106° C.

The field effect type organic transistor was prepared through the stepsbelow. A solution of azobenzene compound A in toluene (0.1 g/mL) wasapplied on a silicon substrate by spin coating, and dried at 80° C. for6 hours. The resulting thin film was heated to 120° C., and cooled toroom temperature. The thin film was irradiated with light of wavelength436 nm in an irradiation energy quantity of 10 J/cm², and then withpolarized light of wavelength 365 nm in an irradiation energy quantityof 1 J/cm². Thereon, gold (50 nm) was vacuum-deposited to form both thesource electrode and the drain electrode having respectively a channellength of 20 μm and a channel width of 50 mm. The both electrodes areformed so as to allow the charges to flow in the direction parallel tothe polarization direction of the irradiating light. Thereon, an organicsemiconductor layer was formed by depositing copper phthalocyanine at apressure of 4×10⁻⁶ torr from a sublimation metal boat placed 10 cm apartfrom the objective substrate at an average deposition rate of 0.1 nm/sat a substrate temperature of 120° C. to a deposition film thickness of100 nm. Further, each of the gate electrode, the drain electrode, andthe source electrode were wired by gold streaks of 0.1 mm diameter bysilver paste. Thus the field effect type organic transistor wascompleted.

The orientation of the organic semiconductor layer was confirmed byexamination by polarization microscopy.

Next, the drain current was measured at the gate electrode ranging from0 to −50 V and the voltage between the source electrode and the drainelectrode ranging from 0 to −50 V. The mobility p was calculatedaccording to Formula (I) shown before. The on-off ratio was derived byapplying voltage of −30 V between the source electrode and the drainelectrode and taking the ratio of the drain current at the gate voltageVg=−30 V to the drain current at the gate voltage Vg=0. The results areshown below.Mobility μ=9.2×10⁻³ cm² /VsOn-off ratio=10⁶

COMPARATIVE EXAMPLE 1

A field effect type organic transistor was prepared in the same manneras in Example 1 except that the light was not applied in formation ofthe gate insulating layer.

The orientation of the organic semiconductor layer was examined bypolarization microscopy, and found to be random. The evaluation wasconducted in the same manner as in Example 1. The mobility and theon-off ratio are shown below.Mobility μ=8.9×10⁻⁵ cm² /VsOn-off ratio=10⁴

EXAMPLE 2

FIG. 3 is a schematic sectional view of the field effect type organictransistor employed in the example of the present invention. Gateelectrode 31 was a highly doped n-type silicon substrate, gateinsulating layer 32 was comprised of SiO₂, source electrode 34 and drainelectrode 35 were comprised of gold, and organic semiconductor layer 36was comprised of dimethylsexithiophene shown by the formula below.

The dimethylsexithiophene was synthesized according to the methoddescribed in “Advanced Materials”, 5, 896, 1993.

Gate insulating layer 33 was comprised of cinnamoyl compound B shownbelow.

The cinnamoyl compound B was synthesized according to the synthesismethod described in “SID'98, Digest”, 780, 1998.

The field effect type organic transistor was prepared through the stepsbelow. A thermal oxidation film SiO₂ (300 nm) was formed on a siliconsubstrate. The surface thereof was treated with3-aminopropyltriethoxysilane, and cinnamoyl chloride was allowed toreact therewith to form the cinnamoyl compound B. The film wasirradiated with polarized light of wavelength 365 nm in an irradiationenergy quantity of 1 J/cm². Thereon, gold (50 nm) was vacuum-depositedto form both the source electrode and the drain electrode havingrespectively a channel length of 20 μm and a channel width of 50 mm. Theboth electrodes are formed so as to allow the charges to flow in thedirection parallel to the polarization direction of the irradiatinglight. Thereon, an organic semiconductor layer was formed by depositingdimethylsexithiophene at a pressure of 5×10⁻⁶ torr from a sublimationmetal boat placed 10 cm apart from the objective substrate at an averagedeposition rate of 0.05 nm/s at a substrate temperature of 25° C. to adeposition film thickness of 100 nm. Further, the gate electrode, thedrain electrode, and the source electrode were wired by gold streaks of0.1 mm diameter by silver paste. Thus the field effect type organictransistor was completed.

The orientation of the organic semiconductor layer was confirmed byexamination by polarization microscopy.

The evaluation was made in the same manner as in Example 1, and themobility and the on-off ratio were calculated. The results are shownbelow.Mobility μ=8.3×10² cm² /VsOn-off ratio=20⁷

COMPARATIVE EXAMPLE 2

A field effect type organic transistor was prepared in the same manneras in Example 2 except that the light was not applied in formation ofthe gate insulating layer.

The orientation of the organic semiconductor layer was examined bypolarization microscopy, and found to be random. The evaluation was madein the same manner as in Example 1, and the mobility and the on-offratio were calculated. The results are shown below.Mobility μ=4.2×10⁻⁴ cm² /VsOn-off ratio=10⁵

EXAMPLE 3

FIG. 2 is a schematic sectional view of the field effect type organictransistor employed in the example of the present invention. Gateelectrode 21 was a highly doped n-type silicon substrate, sourceelectrode 23 and drain electrode 24 were comprised of gold, and organicsemiconductor layer 25 was comprised of pentacene shown by the formulabelow.

Gate insulating layer 22 was comprised of a coumarine compound C shownbelow.

The coumarine compound C had a weight-average molecular weight of7.3×10⁴, and a Tg of 91° C.

The field effect type organic transistor was prepared through the stepsbelow. A solution of coumarine compound C in chloroform (0.1 g/mL) wasapplied on a silicon substrate by spin coating, and dried at 80° C. for6 hours. The resulting thin film was heated to 120° C., and cooled toroom temperature. The thin film was irradiated with polarized light ofwavelength 365 nm in an irradiation energy quantity of 10 J/cm². Thereongold (50 nm) was vacuum-deposited to form both the source electrode andthe drain electrode having respectively a channel length of 20 μm and achannel width of 50 mm. The both electrodes are formed so as to allowthe charges to flow in the direction parallel to the polarizationdirection of the irradiating light. Thereon, an organic semiconductorlayer was formed by depositing pentacene at a pressure of 6×10⁻⁶ torrfrom a sublimation metal boat placed 10 cm apart from the objectivesubstrate at an average deposition rate of 0.1 nm/s at a substratetemperature of 25° C. to a deposition film thickness of 100 nm. Further,the gate electrode, the drain electrode, and the source electrode werewired by gold streaks of 0.1 mm diameter by silver paste. Thus the fieldeffect type organic transistor was completed.

The orientation of the organic semiconductor layer was confirmed byexamination by polarization microscopy.

The evaluation was made in the same manner as in Example 1, and themobility and the on-off ratio were calculated. The results are shownbelow.Mobility μ=6.3×10⁻¹ cm² /VsOn-off ratio=10⁸

EXAMPLE 4

FIG. 2 is a schematic sectional view of the field effect type organictransistor employed in the example of the present invention. Gateelectrode 21 was a highly doped n-type silicon substrate, sourceelectrode 23 and drain electrode 24 were comprised of gold, and organicsemiconductor layer 25 was comprised of copper phthalocyanine. Gateinsulating layer 22 was comprised of a chalcone compound D shown below.

The chalcone compound D had a weight-average molecular weight of6.1×10⁵, and a Tg of 81° C.

The field effect type organic transistor was prepared through the stepsbelow. A solution of chalcone compound D in chloroform (0.1 g/mL) wasapplied on a silicon substrate by spin coating, and dried at 60° C. for6 hours. The resulting thin film was heated to 120° C., and cooled toroom temperature. The thin film was irradiated with polarized light ofwavelength 365 nm in an irradiation energy quantity of 10 J/cm². Thereongold (50 nm) was vacuum-deposited to form both the source electrode andthe drain electrode having respectively a channel length of 20 μm and achannel width of 50 mm. The both electrodes are formed so as to allowthe charges to flow in the direction parallel to the polarizationdirection of the irradiating light. Thereon, an organic semiconductorlayer was formed by depositing copper phthalocyanine at a pressure of4×10⁻⁶ torr from a sublimation metal boat placed 10 cm apart from theobjective substrate at an average deposition rate of 0.1 nm/s at asubstrate temperature of 120° C. to a deposition film thickness of 100nm. Further, the gate electrode, the drain electrode, and the sourceelectrode were wired by gold streaks of 0.1 mm diameter by silver paste.Thus the field effect type organic transistor was completed.

The orientation of the organic semiconductor layer was confirmed byexamination by polarization microscopy.

The evaluation was made in the same manner as in Example 1, and themobility and the on-off ratio were calculated. The results are shownbelow.Mobility μ=1.1×10⁻² cm² /VsOn-off ratio=10⁶

EXAMPLE 5

FIG. 3 is a schematic sectional view of the field effect type organictransistor employed in the example of the present invention. Gateelectrode 31 was a highly doped n-type silicon substrate, gateinsulating layer 32 was comprised of SiO₂, source electrode 34 and drainelectrode 35 were comprised of gold, and organic semiconductor layer 36was comprised of stereotactic poly-3-hexylthiophene shown by the formulabelow.

Gate insulating layer 33 was comprised of cinnamoyl compound B.

The field effect type organic transistor was prepared through the stepsbelow. A thermal oxidation film SiO₂ (300 nm) was formed on a siliconsubstrate. The surface thereof was treated with3-aminopropyltriethoxysilane, and cinnamoyl chloride was allowed toreact to form the cinnamoyl compound B. The film was irradiated withpolarized light of wavelength 365 nm in an irradiation energy quantityof 1 J/cm². Thereon, gold (50 nm) was vacuum-deposited to form both thesource electrode and the drain electrode having respectively a channellength of 20 μm and a channel width of 50 mm. The both electrodes areformed so as to allow the charges to flow in the direction parallel tothe polarization direction of the irradiating light. Thereon, an organicsemiconductor layer was formed by applying a solution of stereotacticpoly-3-hexylthiophene in chloroform (0.01 g/mL) by spin-coating. Thegate electrode, the drain electrode, and the source electrode were wiredby gold streaks of 0.1 mm diameter by silver paste. Thus the fieldeffect type organic transistor was completed.

The orientation of the organic semiconductor layer was confirmed byexamination by polarization microscopy.

The evaluation was made in the same manner as in Example 1, and themobility and the on-off ratio were calculated. The results are shownbelow.Mobility μ=4.7×10⁻² cm² /VsOn-off ratio=10⁶

COMPARATIVE EXAMPLE 3

A field effect type organic transistor was prepared in the same manneras in Example 5 except that the light was not applied in formation ofthe gate insulating layer. The evaluation was made in the same manner asin Example 1, and the mobility and the on-off ratio were calculated. Theresults are shown below.Mobility μ=7.6×10⁻⁴ cm² /VsOn-off ratio=10³

EXAMPLE 6

FIG. 3 is a schematic sectional view of the field effect type organictransistor employed in the example of the present invention. Gateelectrode 31 was a highly doped n-type silicon substrate, gateinsulating layer 32 was comprised of SiO₂, source electrode 34 and drainelectrode 35 were comprised of gold, and organic semiconductor layer 36was comprised of poly-3,4-ethylenedioxythiophene shown by the formulabelow.

Gate insulating layer 33 was comprised of cinnamoyl compound B.

The field effect type organic transistor was prepared through the stepsbelow. A thermal oxidation film SiO₂ (300 nm) was formed on a siliconsubstrate. The surface thereof was treated with3-aminopropyltriethoxysilane, and cinnamoyl chloride was allowed toreact therewith to form the cinnamoyl compound B. The film wasirradiated with polarized light of wavelength 365 nm in an irradiationenergy quantity of 1 J/cm². Thereon, gold (50 nm) was vacuum-depositedto form both the source electrode and the drain electrode havingrespectively a channel length of 20 μm and a channel width of 50 mm. Theboth electrodes are formed so as to allow the charges to flow in thedirection parallel to the polarization direction of the irradiatinglight. Thereon, an organic semiconductor layer was formed by applying asolution of poly-3,4-ethylenedioxythiophene in tetrahydrofuran (0.01g/mL) by spin-coating. The gate electrode, the drain electrode, and thesource electrode were wired by gold streaks of 0.1 mm diameter by silverpaste. Thus the field effect type organic transistor was completed.

The orientation of the organic semiconductor layer was confirmed byexamination by polarization microscopy.

The evaluation was made in the same manner as in Example 1, and themobility and the on-off ratio were calculated. The results are shownbelow.Mobility μ=9.8×10⁻² cm² /VsOn-off ratio=10⁷

This application claims priority from Japanese Patent Application No.2003-328525 filed on Sep. 19, 2003, which is hereby incorporated byreference herein.

1. A field effect type organic transistor comprising a source electrode,a drain electrode, a gate electrode, a gate insulating layer, and anorganic semiconductor layer, wherein the gate insulating layer containsan optical anisotropic material having an anisotropic structure formedby light irradiation, and the organic semiconductor layer is provided incontact with the anisotropic structure.
 2. The field effect type organictransistor according to claim 1, wherein the anisotropic structure isformed by optical isomerization or dimerization.
 3. The field effecttype organic transistor according to claim 1, wherein the opticalanisotropic material is an azobenzene compound, a cinnamoyl compound, acoumarine compound, or a chalcone compound.
 4. The field effect typeorganic transistor according to claim 1, wherein the organicsemiconductor layer is constituted of a conjugated polymer compound. 5.The field effect type organic transistor according to claim 4, whereinthe conjugated polymer compound has a weight-average molecular weightranging from 5,000 to 500,000.
 6. A process for producing a field effecttype organic transistor having a source electrode, a drain electrode, agate electrode, a gate insulating layer, and an organic semiconductorlayer, the process comprising the step of: forming the gate insulatinglayer containing an optical anisotropic material, and forming theorganic semiconductor layer in contact with an anisotropic structureformed by irradiation of light to the optical anisotropic material. 7.The process according to claim 6, wherein the irradiating light isultraviolet light.
 8. The process according to claim 6, wherein theirradiating light is polarized ultraviolet light.